The present invention relates to a perpendicular magnetic anisotropy alloy, a magneto-optical recording layer made of the alloy and a magneto-optical disk adopting the layer, and more particularly, to an amorphous alloy of light rare earth-transition metal and a semi-metal (metalloid), a magneto-optical recording layer made of the amorphous alloy, which exhibits excellent magneto-optical characteristics in a short wavelength range, and a magneto-optical disk adopting the layer.
A magneto-optical disk has high storage density compared to a conventional magnetic disk, and random access characteristics for facilitated searches. Thus, the magneto-optical disk is looked to as a high density recording medium which can replace the hard disk and the magnetic tape.
In a conventional method, the recording layer of the magneto-optical disk is manufactured by depositing a binary alloy of heavy rare earth-transition metal (HRE-TM) having a perpendicular magnetic easy axis with respect to the surface of the recording layer by using a sputtering or vapor deposition method.
When terbium iron (TbFe) or terbium cobalt (TbCo) is used as the binary RE-TM alloy, a strong coercive force and enough magneto-optical effects can be attained. However, corrosion resistance is low.
To overcome the above problems, an alloy of the above binary alloy and another metal has been used as the material for the magneto-optical recording layer, which will be described in detail with reference to FIG. 1.
A ternary amorphous alloy of terbium iron cobalt (TbFeCo), which is excellent in the stability of information storage. However, it is suitable only for long wavelength laser beams (700.about.1,000 nm). Thus, when the amorphous TbFeCo alloy is used in the short wavelength region of 400 nm for improving the magneto-optical recording density, Kerr rotation angle is decreased at the short wavelength region due to the transition of the electron of heavy rare earth metal Tb at a low energy level (i.e., long wavelength), from 4f to 5d, as shown in FIG. 1, thereby reducing the Kerr rotation angle. The decrease of the Kerr rotation angle lowers a carrier-to-noise ratio (CNR) which represents reproducing characteristics of the magneto-optical recording media. Thus, the amorphous alloy of TbFeCo is not desirable as the material for the recording layer of the recording medium in short wavelengths for high density recording.
To solve the above problems, an alloy of light rare earth-transition metal (LRE-TM) of neodymium iron cobalt (NdFeCo) which increases the Kerr rotation angle in the short wavelength region as shown in FIG. 1 has attracted attention as the material for the recording layer of a magneto-optical recording medium in short wavelengths. However, since the alloy of NdFeCo is ferro-magnetically coupled, the demagnetizing energy is high. Thus, the alloy of NdFeCo does not have perpendicular magnetic anisotropy to the surface of a recording layer, so that the alloy cannot be used as material for the recording layer of the magneto-optical recording medium in short wavelengths.
To solve the above problem, the light rare earth metal has been partially substituted with a heavy rare earth metal. That is, an amorphous alloy of neodymium terbium iron cobalt (NdTbFeCo) has been developed in which the ferro-magnetic coupling is partially substituted by a ferri-magnetic coupling to decrease the demagnetizing energy, so that perpendicular magnetic anisotropy to the surface of a recording layer can be induced. However, in the case of the alloy of NdTbFeCo, the Kerr rotation angle is reduced in the short wavelength region as much as the magnetic moment of the light rare earth metal substituted by the heavy rare earth metal, as shown in FIG. 1.